4D-CT is typically used to characterize the tumor motion over the course of the radiotherapy. However, 4D-CT is an oversimplified snapshot representation of a single-breathing cycle with low soft tissue contrast while imparting a considerable amount of radiation dose to the patient. Consequently, the limitations of 4D-CT prevent applicability in acquiring information over timescales that represent a treatment session. MRI is highly advantageous as it is non-ionizing and provides excellent soft tissue contrast. Although real-time 3D dynamic MRI is limited by low image quality and temporal resolution, 2D dynamic MRI techniques have high fidelity and spatio-temporal resolution requisite for real-time tracking of the moving target. Furthermore, a respiration-correlated 4D-MRI can be reconstructed from multi-slice 2D dynamic MR images, enabling volumetric image processing and analysis. Therefore, 4D-MRI is an attractive solution to address breathing motion and tumor tracking obstacles in radiotherapy.